BMS circuit suitable for small-number series battery system
By designing a BMS circuit suitable for small number of series battery systems, using MCU to control the voltage divider circuit and equalization circuit, the existing BMS circuit is solved and the problem of high cost and inability to shut down is achieved, and low-cost and zero-power battery management is achieved.
Patent Information
- Application Number
- CN202421862938.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-02
- Publication Date
- 2025-05-27
- Estimated Expiration
- 2034-08-02
AI Technical Summary
When managing small number of series battery systems, existing BMS circuits are costly and cannot completely shut down the system, resulting in long-term low current discharge being fatal to the battery pack and may cause the battery pack to be scrapped.
A BMS circuit suitable for small number of series battery systems is designed. The voltage divider circuit and equalization circuit are controlled by the MCU to realize the status monitoring and protection of the battery pack, avoiding the use of expensive AFE analog front-end chips, and can consume zero power in the shutdown state.
The cost of the BMS circuit is reduced, the battery pack is scrapped due to low current discharge during long-term storage, and the zero power consumption is achieved in the shutdown state.
Smart Images
Figure CN222915702U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of batteries, in particular to a BMS circuit applicable to a small-number series battery system. Background Art
[0002] BMS is called battery nanny or battery steward, mainly for intelligently managing and maintaining each battery unit, monitoring the state of the battery, preventing the battery from overcharging and over-discharging, so as to extend the service life of the battery; the necessary circuits of the BMS battery management system include: a circuit for collecting the voltage information of each string of batteries, a circuit for collecting the charging current of the battery pack, a circuit for collecting the discharging current of the battery pack, a circuit for collecting the internal temperature of the battery pack, a circuit for equalizing the discharge of each string of batteries, a circuit for overcharge protection of the battery pack during charging, a circuit for over-discharge protection of the battery pack during discharging, etc.
[0003] The current conventional practice for this series of circuits is to use a dedicated AFE analog front-end chip for the BMS battery management system and supplement it with some peripheral circuits; its advantages are high integration and high measurement accuracy, but there are also certain disadvantages, that is, high cost and inability to allow the complete shutdown of the system, that is, it will consume the energy of the battery pack at any time. Especially the last point is unacceptable in some special occasions. For example, for some products that need to be stored for a long time, long-term low-current discharge is fatal to the battery pack and will seriously cause the entire battery pack to be scrapped. Summary of the Utility Model
[0004] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a BMS circuit applicable to a small-number series battery system, solving the deficiencies existing in the prior art.
[0005] The purpose of the utility model is realized through the following technical solutions: a BMS circuit applicable to a small-number series battery system, the BMS circuit includes a battery pack composed of N strings of batteries connected in series, and N≤6. The terminal voltage of each string of batteries is connected to a voltage-dividing circuit, and the output end of the voltage-dividing circuit is connected to the ADC interface of the MCU. The IO port of the MCU is connected to the input end of the voltage-dividing circuit, and then controls the switch tube in the voltage-dividing circuit to conduct, and the voltage input to the MCU in the fully charged state of the battery pack is set within the VREF range of the MCU and close to VREF through the voltage-dividing circuit;
[0006] Each string of batteries is also connected in parallel with an equalizing circuit, the equalizing circuit is connected to the MCU, and the equalization of the corresponding battery is realized by controlling the equalizing circuit by the MCU; the MCU is connected to a voltage-regulating chip U4, and the voltage-regulating chip U4 is connected to a switch J1. When the switch J1 is pressed, the voltage-regulating chip U4 is powered on to output VCC to make the MCU start working;
[0007] The negative electrode of the battery pack is connected to a current sampling resistor and an amplifier follower circuit in parallel with the current sampling resistor. The MCU controls two MOS transistors to conduct, thereby connecting the system load to both ends of the battery pack, and forming a voltage BAT- at the current sampling resistor end. The CURR voltage is obtained through the amplifier follower circuit and sent to the MCU. The charging current and discharging current of the current sampling resistor are calculated based on the amplifier follower circuit. When the charging current exceeds the set charging protection current value or the discharging current exceeds the set discharging current protection value, the MCU controls the two MOS transistors to disconnect to protect the battery pack.
[0008] The voltage dividing circuit includes a MOS transistor, a first voltage dividing resistor, and a second voltage dividing resistor; the positive electrode of each string of batteries is connected to the drain of the MOS transistor, the source of the MOS transistor is connected to the series-connected first voltage dividing resistor and the second voltage dividing resistor, and the ADC interface of the MCU is connected to the series connection end of the two voltage dividing resistors. By calculating the ratio of the first voltage dividing resistor and the second voltage dividing resistor, the voltage input to the MCU in the fully charged state of the battery pack is set within the VREF range of the MCU and close to VREF.
[0009] The IO port of the MCU is connected to the base of the first triode through the first resistor, and the collector of the first triode is connected to the gate of the MOS transistor; the IO port of the MCU outputs a high level, and then controls the MOS transistor to conduct through the first resistor and the first triode.
[0010] The amplifier follower circuit includes an operational amplifier amplification circuit and a follower circuit; the operational amplifier amplification circuit includes an operational amplifier chip U1A. The negative electrode of the battery pack is connected to the non-inverting input terminal of the operational amplifier chip U1A through the second resistor, and the output terminal of the operational amplifier chip U1A outputs the CURR voltage to the MCU. The follower circuit is connected to the non-inverting input terminal of the operational amplifier chip U1A through the third resistor.
[0011] The follower circuit includes an operational amplifier chip U3B. The inverting input terminal and the output terminal of the operational amplifier chip U3B are connected. The output terminal is connected to the non-inverting input terminal of the operational amplifier chip U1A through the third resistor. The non-inverting input terminal of the operational amplifier chip U3B is connected in parallel with a fourth resistor and a fifth resistor. The other end of the fourth resistor is connected to the MCU, and the other end of the fifth resistor is grounded; the 1 / 2VREF voltage generated after the ADC voltage reference VREF generated inside the MCU is divided by the fourth resistor and the fifth resistor is sent to the follower composed of the operational amplifier chip U3B, and then the same voltage 1 / 2VREF is sent to the third resistor.
[0012] The balancing circuit includes a second triode, a third triode, and a sixth resistor. The collector of the second triode is connected to the base of the third triode. The collector of the third triode is connected to the negative electrode of the battery through the sixth resistor, and the emitter of the third triode is connected to the positive electrode of the battery. The IO port of the MCU outputs a high level to the base of the second triode, causing the second triode to conduct, and thus causing the third triode to conduct. At this time, the excess energy of this series of batteries is consumed through the third triode and the sixth resistor.
[0013] When the MCU controls the gates of the two MOS transistors to be at a high level at the same time, the two MOS transistors conduct, and the system load is connected to both ends of the battery pack. At this time, the load is powered by a battery pack composed of N series-connected batteries and a voltage BAT- is formed at the current sampling resistor terminal.
[0014] The BMS circuit further includes a temperature detection circuit. The temperature detection circuit includes a thermistor RT1 and a third voltage-dividing resistor connected in series. The other end of the third voltage-dividing resistor is connected to the output terminal of the operational amplifier chip U3B, and the other end of the thermistor RT1 is grounded. The series connection terminal of the thermistor RT1 and the third voltage-dividing resistor is connected to the MCU.
[0015] The present invention has the following advantages: A BMS circuit applicable to a small-number series battery system has greatly reduced costs because it does not use a relatively expensive AFE analog front-end chip dedicated to the BMS battery management system; it also avoids the disadvantage that the AFE chip cannot be powered off and thus continuously consumes power. Description of the Drawings
[0016] Figure 1 is a circuit schematic diagram of the present invention. Detailed Embodiments
[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Usually, the components of the embodiments of the present application described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the protection scope of the present application that is required to be protected, but only represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application. The present invention will be further described below with reference to the accompanying drawings.
[0018] The present utility model specifically relates to a BMS circuit with low cost and zero consumption in the shutdown state for a small number of series battery systems. The number of series-connected batteries is between 2 and 4 strings, and at most does not exceed 6 strings. For example, Figure 1 as shown, the present utility model will be described with a 4-series battery system.
[0019] B1, B2, B3, and B4 are connected in series to form a battery pack; the voltage at the B1 terminal is controlled by Q1 to access the voltage-dividing circuit composed of R2 and R5, and is connected to the ADC interface of the MCU through BATV4; the voltage at the B2 terminal is controlled by Q5 to access the voltage-dividing circuit composed of R11 and R14, and is connected to the ADC interface of the MCU through BATV3; the voltage at the B3 terminal is controlled by Q9 to access the voltage-dividing circuit composed of R20 and R23, and is connected to the ADC interface of the MCU through BATV2; the voltage at the B4 terminal is controlled by Q13 to access the voltage-dividing circuit composed of R29 and R32, and is connected to the ADC interface of the MCU through BATV1.
[0020] Among them, the control of Q1 is that the IO port of the MCU controls TV4 to pull high, and then R6 and Q2 control Q1 to conduct; the control of Q5 is that the IO port of the MCU controls TV3 to pull high, and then R15 and Q6 control Q5 to conduct; the control of Q9 is that the IO port of the MCU controls TV2 to pull high, and then R24 and Q10 control Q9 to conduct; the control of Q13 is that the IO port of the MCU controls TV1 to pull high, and then R33 and Q14 control Q13 to conduct; by calculating the ratio of R2 and R5, the BATV4 voltage under the full-charge state of the battery pack can be set within the VREF range of the MCU and close to VREF; by calculating the ratio of R11 and R14, the BATV3 voltage under the full-charge state of the battery pack can be set within the VREF range of the MCU and close to VREF; by calculating the ratio of R20 and R23, the BATV2 voltage under the full-charge state of the battery pack can be set within the VREF range of the MCU and close to VREF; by calculating the ratio of R29 and R32, the BATV1 voltage under the full-charge state of the battery pack can be set within the VREF range of the MCU and close to VREF.
[0021] Further, R42 is a high-power milliohm-level current sampling resistor; when the MCU simultaneously controls DSG and CHG to be at a high level, Q17 and Q18 conduct, the positive pole of the system load is connected to P+, and the negative pole of the system load is connected to P-. At this time, the load can obtain energy from the battery pack composed of B1, B2, B3, and B4 to work, and a voltage BAT- is formed at the R42 terminal. The BAT- voltage is amplified by an operational amplifier and then the CURR voltage is sent to the ADC port of the MCU; BAT- = -R42 * discharge current;
[0022] When the MCU controls DSG and CHG to be at high level simultaneously, Q17 and Q18 conduct, the positive terminal of the charger is connected to CHG+, the negative terminal of the charger is connected to CHG-, a voltage (BAT-) is formed at the R42 terminal, and after being amplified by the operational amplifier, the CURR voltage is sent to the MCU; BAT- = (R42) * charging current; Since the ADC voltage reference VREF generated inside the MCU is divided by R43 and R45 with the same resistance value to generate a 1 / 2VREF voltage, which is sent to the follower composed of operational amplifier U3B, and the same 1 / 2VREF voltage is sent to R38. The result is that when there is no load current and charging current, the output voltage CURR of operational amplifier U1A is 1 / 2VREF. When there is a load current, CURR = 1 / 2VREF - (BAT-) * (R44 + R41) / R41. When there is a charging current, CURR = 1 / 2VREF + (BAT-) * (R44 + R41) / R41; Finally, through the above relationships, the BAT- voltage can be calculated, and then the charging current and discharging current can be obtained; When the charging current exceeds the set charging protection current value or the discharging current exceeds the set discharging current protection value, the IO port of the MCU pulls down DSG and CHG to achieve the purpose of protecting the battery pack.
[0023] Through the above relationships, it can be obtained that: (B4 voltage) = BATV1 * (R29 + R32) / R32 - (BAT-), (B3 voltage) = BATV2 * (R20 + R23) / R23 - (B4 voltage) - (BAT-), (B2 voltage) = BATV3 * (R11 + R14) / R14 - (B4 voltage) - (B3 voltage) - (BAT-), B1 voltage = BATV4 * (R2 + R5) / R5 - (B4 voltage) - (B3 voltage) - (B2 voltage) - (BAT-).
[0024] After obtaining the voltage of each battery cell, when it is found that the voltage of a certain battery cell exceeds a certain voltage of the battery cell with the lowest voltage, and at an appropriate time, balancing can be carried out; for example, if the voltage of B4 is high and needs to be balanced, the IO port of the MCU will pull up BAL1 to turn on Q16, and then Q15 will be turned on, and the excess energy of B4 will be consumed through Q15 and R35; if the voltage of B3 is high, the IO port of the MCU will pull up BAL2 to turn on Q12, and then Q11 will be turned on, and the excess energy of B3 will be consumed through Q11 and R26; if the voltage of B2 is high, the IO port of the MCU will pull up BAL3 to turn on Q8, and then Q7 will be turned on, and the excess energy of B2 will be consumed through Q7 and R17; if the voltage of B1 is high, the IO port of the MCU will pull up BAL4 to turn on Q4, and then Q3 will be turned on, and the excess energy of B1 will be consumed through Q3 and R8; the above process stops when the voltage difference between each battery cell is less than a certain value, or when other conditions unsuitable for the balancing operation occur; in addition, to ensure the stable operation of the system, generally, the balancing operation is not allowed to be carried out on adjacent battery cells at the same time, so only odd-numbered or even-numbered battery cells will be operated simultaneously during operation.
[0025] When charging, when the voltage of a certain battery cell exceeds the charging cut-off voltage, the MCU turns off the charging circuit by pulling down DSG and CHG to protect the battery pack; when discharging, when the voltage of a certain battery cell is lower than the discharging cut-off voltage, the MCU turns off the discharging circuit by pulling down DSG and CHG to protect the battery pack.
[0026] The temperature of the battery pack is detected by a thermistor RT1. Specifically, the VREF voltage is divided by R46 and RT1 to obtain the TEMP voltage, and the MCU can calculate the temperature by measuring TEMP; when the temperature of the battery pack exceeds a certain set value and is lower than a certain set value, the MCU turns off the discharging or charging circuit by pulling down DSG and CHG to protect the battery pack.
[0027] As can be seen from the above circuit, the energy of the battery pack is only consumed when the MCU's IO port pulls up DSG and CHG to discharge the load, or when the MCU's IO port pulls up TV1, TV2, TV3, and TV4 to measure the battery terminal voltage, or when the MCU's IO port pulls up BAL1, BAL2, BAL3, and BAL4 to balance the battery, and when the voltage regulator chip U4 is working; if the MCU pulls down POWER_HOLD, Q20 turns off, Q19 turns off, U4 stops working, VCC disappears, the MCU stops working, and no longer consumes the energy of the battery pack. At this time, all ports of the MCU are in the low-level state, and all parts of the system no longer consume electrical energy, that is, the system is in a zero-power consumption state; if you need to turn on the system again, just press the switch J1. At this time, Q20 conducts, and then Q19 conducts. The voltage regulator chip U4 gets power and outputs VCC. The MCU starts to work and immediately pulls up the IO port POWER_HOLD. Even after J1 is released and powered off, since POWER_HOLD continuously provides voltage, the system will maintain the operating state.
[0028] Since the voltage of each battery is not directly measured, but calculated using the relative relationship of the circuit, the ADC resolution of the MCU needs to reach at least 12 bits, and the conversion speed needs to be relatively high. Therefore, this circuit is not recommended to operate with more than 6 strings. Otherwise, the measured battery voltage accuracy is relatively low, and the operating effect is not good; for example, in a 4-series lithium iron phosphate battery system, the terminal voltage can reach up to 4 * 3.7V = 14.8V. Measured with a 12-bit ADC, the minimum can be resolved to about 14.8V / 4096, about 3.6mV. Considering factors such as system error, the final resolution can reach about 6mV. In a system with not too high balancing requirements, it can already meet the requirements well.
[0029] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and improvements, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. And the changes and modifications made by those skilled in the art that do not depart from the spirit and scope of the present invention should all be within the protection scope of the appended claims of the present invention.
Claims
1. A BMS circuit suitable for a small number of series-connected battery systems, characterized in that: The BMS circuit includes a battery pack consisting of N battery strings connected in series, where N is less than or equal to 6. The voltage at the end of each battery string is connected to a voltage divider circuit. The output end of the voltage divider circuit is connected to the ADC interface of the MCU. The IO port of the MCU is connected to the input end of the voltage divider circuit, thereby controlling the conduction of the switch tube in the voltage divider circuit. The voltage input to the MCU when the battery pack is fully charged is set within the VREF range of the MCU and close to VREF through the voltage divider circuit. Each battery string is also connected in parallel with a balancing circuit, which is connected to the MCU. The balancing circuit is controlled by the MCU to achieve the balancing of the corresponding battery. The MCU is connected to the voltage stabilizing chip U4, which is connected to a switch J1. When the switch J1 is pressed, the voltage stabilizing chip U4 is powered and outputs VCC to start the MCU working. The negative pole of the battery pack is connected to a current sampling resistor and an amplifier-follower circuit connected in parallel with the current sampling resistor. The MCU controls the two MOS tubes to be turned on, thereby connecting the system load to the two ends of the battery pack and forming a voltage BAT- at the end of the current sampling resistor. The CURR voltage is obtained through the amplifier-follower circuit and sent to the MCU. The charging current and discharging current of the current sampling resistor are calculated according to the amplifier-follower circuit. When the charging current exceeds the set charging protection current value or the discharging current exceeds the set discharge current protection value, the MCU controls the two MOS tubes to be disconnected to protect the battery pack.
2. A BMS circuit suitable for a small number of series-connected batteries according to claim 1, characterized in that: The voltage-dividing circuit includes a MOS tube, a first voltage-dividing resistor and a second voltage-dividing resistor; the positive electrode of each string of batteries is connected to the drain of the MOS tube, the source of the MOS tube is connected to the first voltage-dividing resistor and the second voltage-dividing resistor connected in series, the ADC interface of the MCU is connected to the series end of the two voltage-dividing resistors, and by calculating the ratio of the first voltage-dividing resistor and the second voltage-dividing resistor, the voltage input to the MCU when the battery pack is fully charged is set within the VREF range of the MCU and close to VREF.
3. A BMS circuit suitable for a small number of series-connected batteries according to claim 2, characterized in that: The IO port of the MCU is connected to the base of the first transistor through the first resistor, and the collector of the first transistor is connected to the gate of the MOS tube; the IO port of the MCU outputs a high level, and then controls the MOS tube to be turned on through the first resistor and the first transistor.
4. A BMS circuit suitable for a small number of series-connected battery systems according to claim 1, characterized in that: The amplifier-follower circuit includes an operational amplifier circuit and a follower circuit; the operational amplifier circuit includes an operational amplifier chip U1A, the negative pole of the battery pack is connected to the positive phase input terminal of the operational amplifier chip U1A through a second resistor, the output terminal of the operational amplifier chip U1A outputs a CURR voltage to the MCU, and the follower circuit is connected to the positive phase input terminal of the operational amplifier chip U1A through a third resistor.
5. A BMS circuit suitable for a small number of series-connected batteries according to claim 4, characterized in that: The follower circuit includes an operational amplifier chip U3B, the inverting input terminal of the operational amplifier chip U3B is connected to the output terminal, the output terminal is connected to the non-inverting input terminal of the operational amplifier chip U1A through a third resistor, the non-inverting input terminal of the operational amplifier chip U3B is connected in parallel with a fourth resistor and a fifth resistor, the other end of the fourth resistor is connected to the MCU, and the other end of the fifth resistor is grounded; the ADC voltage reference VREF generated inside the MCU is divided by the fourth resistor and the fifth resistor to generate a 1 / 2VREF voltage which is sent to the follower composed of the operational amplifier chip U3B, and the same voltage 1 / 2VREF generated is sent to the third resistor.
6. A BMS circuit suitable for a small number of series-connected battery systems according to claim 1, characterized in that: The balancing circuit includes a second triode, a third triode and a sixth resistor, the collector of the second triode is connected to the base of the third triode, the collector of the third triode is connected to the negative electrode of the battery through the sixth resistor, and the emitter of the third triode is connected to the positive electrode of the battery; the IO port of the MCU outputs a high level to the base of the second triode, so that the second triode is turned on, thereby turning on the third triode, and at this time, the excess energy of the string of batteries is consumed through the third triode and the sixth resistor.
7. A BMS circuit suitable for a small number of series-connected batteries according to claim 1, characterized in that: When the MCU simultaneously controls the gates of the two MOS tubes to be high level, the two MOS tubes are turned on, and the system load is connected to the two ends of the battery pack. At this time, the load is powered by the battery pack composed of N strings of batteries connected in series, and a voltage BAT- is formed at the end of the current sampling resistor.
8. A BMS circuit suitable for a small number of series-connected batteries according to claim 5, characterized in that: The BMS circuit also includes a temperature detection circuit, which includes a thermistor RT1 and a third voltage-dividing resistor connected in series; the other end of the third voltage-dividing resistor is connected to the output end of the operational amplifier chip U3B, and the other end of the thermistor RT1 is grounded; the series end of the thermistor RT1 and the third voltage-dividing resistor is connected to the MCU.